Method of forming structural panel assemblies

ABSTRACT

The method of forming rigid panel assemblies of this invention eliminates the requirement for mechanical fasteners and may be used to bond wall boards to studs, floor joists to wood flooring such as plywood or OSB boards and trusses to ceiling panels. The method of this invention includes applying a thin bead of a thoroughly mixed two-component liquid polyurethane foamable resin adhesive on the surface where the components are to be joined. The foamable resin is formulated to provide a long tack time or delay curing until the assembly is complete. The foamable resin is then allowed to cream and rise before bonding. Where the bead is applied to the side faces of the support members, the support members are preferably turned to orient the foam beads over the fibrous panel, which is preferably supported on a flat horizontal support surface. Finally, the beads are compressed against the fibrous panel, wetting the panel with liquid foam resin before the foam has gelled, permanently bonding the support members to the panel and forming the structural panel assembly. Where an enclosed panel assembly, such as a closed wall is desired, the structural members are attached to a first panel, orienting the support members for application of the polyurethane foam bead, as described.

This is a continuation of application(s) Ser. No. 08/451,760 filed onMay 26, 1995, now U.S. Pat. No. 5,635,118; which is a continuation ofU.S. Ser. No. 08/407,695 filed on Mar. 21, 1995, now U.S. Pat. No.5,714,099; which is a continuation of U.S. Ser. No. 08/014,440 filed onFeb. 5, 1993 now U.S. Pat. No. 5,425,908 which issued on Jun. 20, 1995.

BACKGROUND OF THE INVENTION

The present invention relates to a method of making prefabricatedrelatively rigid structural panel assemblies, such as prefabricatedwall, flooring and ceiling assemblies used by the prefabricated orfactory built construction industry, such as the manufactured housingindustry. The panels are permanently attached to reinforcing studs,joists or trusses, forming a relatively rigid prefabricated module.Closed well modules include a pair of parallel panels forming the wallsurfaces and a plurality of transverse studs permanently attached to thewall boards.

The method of this invention is particularly, but not exclusively,adapted to a process for making such structural panel assemblies withoutthe requirement of mechanical fasteners, such as nails, staples orscrews to secure the panel to the structural members, which must becovered with batten strips. A problem with the manufacture ofprefabricated wall, floor or ceiling panel assemblies has been that thecomponents are not uniform. The boards used for studs, joists andtrusses do not have a level or straight plane and may have otherdiscrepancies, such as knot holes. The fibrous panels to which suchsupport members are attached are somewhat flexible, but are oftenwarped. Thus, a wall, floor or ceiling panel, which is supported bystuds, joists or trusses attached by mechanical fasteners, is generallyboth warped and spaced from the reinforcing members in many locations.The exposed surface of the mechanical fasteners or clamps must alsogenerally be covered and fasteners pop out after construction because ofinherent assembly and user movement and stresses resulting from thewarped components. These problems can only be partially solved in "stickbuilt" construction, where the wall, floor or ceiling panel assembliesare built entirely on site, by selection of materials, the use of shims,etc. However, factory or pre-built construction preferably utilizes massproduction techniques which do not lend themselves to such hand-madeadjustments.

U.S. Pat. Nos. 4,244,901 and 4,748,781, assigned to the assignee of thisapplication, disclose methods of forming reinforced panel assembliesutilizing polyurethane foam to bond the structural support members tothe panels. In the preferred embodiment, the panel is laid upon a flatsupport surface, the studs or support members are located on the back ofthe panel and clamped. A high pressure stream of a liquid foamable resinis then directed to the juncture of the support members and the panel,such that the resin foams and fills the space between the supportmembers and the panel, permanently bonding the support members to thepanel without mechanical fastening means. This method has beencommercially successful in making prefabricated or factory-builtstructural panels; however this process is not suitable for enclosedpanel construction, such as a closed wall structural assembly.

The method of this invention has advantages over the prior art and issuitable for the manufacture of enclosed panel structures, such asclosed wall assemblies used by the manufactured construction industry.The disclosed method may be substantially automated and utilizes arelatively small amount of foamable resin adhesive. The method of thisinvention may also be used at any temperature normally encountered bythe factory-built construction industry. Upon completion of thereinforced panel assembly, the assembly can be moved almost immediatelyusing conventional mass production material handling techniques.

SUMMARY OF THE INVENTION

As stated, the method of this invention is particularly suited for themanufacture of reinforced structural fibrous panels, such as used by themanufactured construction industry for walls, floors and ceilings. Themethod of this invention may also be adapted for mass productiontechniques utilizing the materials now used by the prefabricated orfactory-built construction industry.

In the method of this invention, the reinforcing members, which may bewall studs, ceiling trusses or floor joists for example are oriented andsupported vertically, such that the relatively thin side faces arelocated at the top of the support members. Where an enclosed structuralassembly, such as a closed wall is to be manufactured, the supportmembers are preferably first attached to one panel and the panel issupported on a horizontal surface, such that the support members extendvertically from the first panel. The support members may be attached tothe first panel by the methods disclosed in the above-referenced U.S.Pat. Nos. 4,244,901 or 4,748,781. As disclosed in U.S. Pat. No.4,748,781, the structural support members may also be metal channels.

The method of this invention then includes applying a thin bead of athoroughly mixed two-component liquid polyurethane foamable resinadhesive axially along the top side surfaces of each of the supportmembers. The foamable resin adhesive must have a relatively long tacktime and is preferably resilient or pliable, having good wettingcharacteristics, green strength and fast reacting with controlled cure,such that the time that the foam remains resilient and tacky can beextended and controlled. The preferred foamable resin is of relative lowviscosity and is also thixotropic, such that the resin can be thoroughlymixed in an impingement mixing chamber of an application gun, but suchthat the bead does not run upon application. The foam is then allowed tosubstantially fully cream and rise, forming a liquid foam polyurethanebead. The support surfaces of the support members having the foamedpolyurethane bead are then pressed against the panel to be joined to thesupport members, compressing the polyurethane beads and wetting thepanel, permanently bonding the support members to the panel, withoutrequiring mechanical fasteners or clamps. This must be completed beforethe polyurethane foam beads cure tack free or the polyurethane foam willnot wet the surface of the panel and bond sufficiently.

In certain applications, such as where the application gun is computercontrolled, it may be desirable to apply the foam bead to the panelfirst, rather than the support members. In such an application, thepanel will be laid upon a flat support surface. A predetermined patternof polyurethane beads are then applied to the panel with the pattern ofbeads corresponding to the desired locations for the support members.Where a double walled structure is to be made, the structural supportmembers are first applied to a second panel, as described, or thesupport members may be supported in a fixture. The side faces of thesupport members are then applied to the polyurethane beads, permanentlybonding the structural support members to the panel, as described.

In the most preferred method, the panel which is to be bonded to thesupport members is first laid upon a flat horizontal support surface.After applying the bead to the support members, the support members areturned or rotated to orient the surface having the polyurethane foambead downwardly over the flat panel and the support surfaces are thenpressed against the panel to compress the foam beads, wetting the panelsurface and permanently bonding the support members to the panel. Thefoam beads thus ,fill in any imperfections or warped areas of thereinforcing support members and the panel remains flat followingattachment of the support members. Further, neither the panel nor thesupport members are stressed during attachment and no mechanicalfastening means is required.

The polyurethane foam bead is preferably applied axially alongsubstantially the entire length of the reinforcing support members at arelatively slow forward velocity to avoid splatter and assure a goodbond between the structural reinforcing members and the panel. To avoidsplatter, the gun should be moved at about the forward velocity of theresin exiting the gun. A liquid resin bead having a width of about 1/4inch applied at an application rate of less than about 3 feet per secondhas been found suitable for most hand applications. A two-componentliquid foamable polyurethane resin adhesive is also preferred. Thefoamable resin adhesive should be relatively slow acting and theformulation is preferably adjustable to accommodate the environment ofthe application. In the most preferred embodiment, the liquidpolyurethane foamable resin begins to cream almost immediately andsubstantially fully rises within a few minutes, such that the foam beadis ready for bonding, as described. The foam bead must be pressedagainst the panel or structural member before the foam cures or the foamwill not satisfactorily wet and bond sufficiently. Thus, thepolyurethane foam should be formulated for the particular application.In the most preferred embodiment, the foam fully rises quickly, but thefoam does not cure tack free for at least 10 minutes and may, ifpreferred, not cure for about 20 minutes. In most preferredapplications, a polyurethane foam which cures in 15 to 20 minutes hasbeen found to be particularly suitable for mass production applications.

The method of making a structural panel assembly of this invention isthus particularly suitable for the manufacture of prefabricated orfactory-built reinforced fibrous panel assemblies, including rigidenclosed panel assemblies, such as closed wall modules used by theconstruction industry. A closed wall assembly may be built by the methodof this invention without using mechanical fasteners or clamps and bothwalls may be substantially perfectly flat using mass productiontechniques. The reinforced wall construction may be handled usingindustrial mass handling techniques almost immediately upon completionof the bond and without requiring clamps. Other advantages andmeritorious features of the method of this invention will be more fullyunderstood from the following description of the preferred embodiments,the appended claims and the drawings, a brief description of whichfollows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a panel assembly illustrating theapplication of a foam bead on the structural support members;

FIG. 2 is a partial end view of a structural support member immediatelyafter the application of a bead of liquid foamable resin adhesive;

FIG. 3 is a partial end view of a structural support member, similar toFIG. 2, after the bead has substantially fully creamed and risen;

FIG. 4 is an end view of a structural support member bonded to a finishpanel;

FIG. 5 is a top perspective view illustrating a preferred method ofapplying the structural support members to the finish panel;

FIG. 6 is a side view of a rigid structural panel assembly formed by themethod of this invention;

FIG. 7 is another side view of a rigid structural panel assembly formedby the method of this invention;

FIG. 8 is a side view of an impingement mixing chamber of a foamapplication gun suitable for use in the method of this invention; and

FIG. 9 is a side cross-sectional view of the mixing chamber shown inFIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE METHOD OF THIS INVENTION

As described above, the method or process of this invention isparticularly suitable for making structural panel assemblies withoutrequiring mechanical fasteners or clamps. The method of this inventionwill form panel assemblies having a completely flat finish panel,although the structural support members are warped or irregular and thepanel was initially warped or "wowed." The structural panel assemblieswhich may be formed by the method of this invention, includeprefabricated wall, flooring and ceiling assemblies, such as used by themanufactured housing, recreational vehicle and prefabricated industrialbuilding industries. The method of this invention may also be used tomake closed wall modules having parallel panels supported by studspermanently adhesively bonded to the panels.

FIG. 1 illustrates a method of forming a first panel assembly 20 as maybe utilized in the method of this invention. As shown, the panelassembly 20 includes a plurality of generally parallel structuralmembers 22a, 22b and 22c which have been secured to a first panel 24 byfoam resin adhesive as described, for example, in the above-referencedU.S. Pat. No. 4,244,901. Such structural support members 22 are commonlyreferred to as studs in wall assemblies, joists in floor assemblies andtrusses in ceiling assemblies. In the disclosed embodiment of the firstpanel assembly 20, the structural support members 22 are wood, such asthe wood 2×4's commonly used for studs in wall assemblies. It will beunderstood, however, that the structural support members 22 may beformed of any material used by the construction industry, including thechannel-shaped metal structural support members disclosed in U.S. Pat.No. 4,748,781 and the structural support members may be secured to thefirst panel 24 by any suitable means, including mechanical fasteners orclamps. However, as described in the above-referenced U.S. patents, thestructural members 22 may be bonded to the first panel 24 by a thin highpressure stream of polyurethane foam adhesive directed to the base ofthe structural members, forming a flat panel assembly.

In the method of this invention, a thin bead 28 of a thoroughly mixedtwo-component liquid polyurethane foamable resin adhesive is applied tothe thin side faces 29 of the structural members which are to be bondedto the finish panel, as described below. As shown, the foamable resinadhesive is applied to the structural members by a foam application gun40. The disclosed embodiment of the foam application gun includes linesor hoses 32a and 32b which receive and deliver the A-isocyanate andB-resin components of the foamable resin adhesive, to an impingementmixing chamber 34 described more fully hereinbelow, a trigger assembly36, a pneumatic cylinder assembly 38 and a manual screw adjustmentassembly 40 which adjusts the throw of the valve rod shown in FIGS. 8and 9. The disclosed embodiment of the application gun 30 is acommercially available Model D spray gun sold by Gusmer Corp. ofLakewood, N.J. Of course, other two-component liquid foamable resinadhesive spray guns having a high velocity impingement mixing chamber ormodule can also be used. Another suitable foam application gun is theModel GX-7 gun having a high impingement module available from GusmerCorp. Although conventional two-component foam spray guns may be used,the gun must be modified or adjusted, as described below, to produce arelatively low forward velocity stream of thoroughly mixed polyurethanefoam resin adhesive to produce a relatively thin bead of foamed resinadhesive for the method of this invention.

In the method disclosed in FIG. 1, a thin foam bead 28a of liquidfoamable resin adhesive is being applied to the top face 29 ofstructural support member 22a by foam application gun 30. The firstpanel assembly 20 may be supported on a horizontal surface or angled toreduce floor space. The gun is preferably moved at about the forwardvelocity of the liquid stream of polyurethane foamable resin adhesiveexiting the application gun 30, such that there is substantially nosplatter. The gun may be hand-held, as shown, or the gun may besupported on an application machine which may be computer controlled. Asshown in FIG. 1, the bead 28a is very thin, as applied. The liquidfoamable resin adhesive bead begins to cream and rise, however, almostimmediately following application, such that the bead is substantiallyfully creamed and expanded as shown at 28b (see FIG. 3) within a fewseconds after application, preferably less than 3 seconds. In a typicalapplication where the foam bead is applied to the thin face of a 2×4inch structural support member, a liquid bead having a width of about1/4 inch upon application has been found to be very effective. The beadthen creams and rises to about double the original height and width, orabout 1/2 inch, as shown at 28b and 28c in FIG. 1 and 28b in FIG. 3.

A two-component polyurethane foamable resin adhesive was especiallyformulated for the method of this invention. As described, the forwardvelocity of the liquid foamable resin adhesive exiting from theapplication gun is relatively low to form a bead without splatter,preferably less than about 5 feet per second or about 1 to 3 feet persecond for hand-held gun applications. The A and B components of thefoamable polyurethane resin must, however, be thoroughly mixed beforeapplication. To achieve thorough mixing, an application gun having arelatively high pressure impingement mixing chamber was selected andused with relatively low viscosity liquid foamable resin components.When applied, however, the foamable resin bead should not run. Toachieve this result, a thixotropic formulation was developed whichbegins to cream and rise almost immediately upon application, but at thesame time has an extended rate of cure time.

Further, as described, the method of this invention is particularlysuitable for forming wall, ceiling and flooring assemblies forprefabricated construction industries, such as the manufactured housingindustry. Thus, the polyurethane foamable resin is preferably formulatedfor use at a relatively wide range of ambient temperatures, preferablybetween about 30 and 100 degrees Fahrenheit. Humidity should notadversely affect the resultant bond. Finally, the method of thisinvention is also suitable for mass production of structural panelassemblies, including automated assembly processes. Thus, the foamableresin adhesive preferably sets up and cures in a controlled manner. Inmost applications, it is preferred that the foamable resin adhesivecures in about 10 to 30 minutes, permitting completion of the assemblybefore the foam beads fully cure tack free. For most applications, thefoamable resin adhesive should fully rise in less than 2 minutes andcure in 15 to 25 minutes at the ambient temperature where the beads areapplied. Of course, the foamable resin adhesive must also provide anexcellent bond between the structural support members and the panel. Toaccomplish good bonding with the method of this invention, the foam beadmust have good wetting characteristics, a relatively long tack time andgood green strength. As described, the reinforced panel assembly formedby the method of this invention can be picked up and handled almostimmediately following completion of the assembly.

Current polyurethane systems used by the factory-built constructionindustry include single component moisture cured polyurethane foams anddual component static mix systems. With the moisture cure process, themanufacturer is limited in its use because the cure/set time varies from0.75 hours to more than 1.5 hours. The dual component polyurethanesystems presently available use a static mix process that is both costlyand involves a solvent flush, such as methylene chloride. With a solventflush, the uses are limited because of environmental problems andhazardous waste disposal requirements. The two-component polyurethanefoamable resin Adhesive of this invention is water blown and mixed inthe application gun, eliminating the requirement for static mixing,solvent cleaning and the like and permitting use in the method of thisinvention.

The following formulation was developed by Applicant for the B polyolside of the resin adhesive:

    ______________________________________    Constituent   Weight Percent    ______________________________________    PG 76-120     90-92%    R 420         4.5-5.5%    L 5420         1.4-1.45%    H.sub.2 O     2.5-2.6%    ______________________________________

PG 76-120 is a polyether polyol available from Olin Corp. PG 76-120 hasimproved wetting characteristics, reduced viscosity and improves theplyability of the polyurethane foam. It also reduces fryability andreduces stryration or crystalization. R 420 is also a polyether polyolavailable from Texaco Chemical Co. which provides improved reactivity. L5420 is a silicone surfactant available from Union Carbide Chemicals &Plastics Co., Inc. The H₂ O is distilled water. The A-isocyanate side ofthe formulation is 100 percent methylene bis 4-phenyl-isocyarateavailable from Miles Inc. and ICI Americas, Inc.

The above formulation is suitable for applications at most ambienttemperatures encountered under production conditions greater than about45° F. At lower ambient temperatures or temperatures between about 30°F. and 65° F., the following formulation has been found to beparticularly suitable for the B polyol side of the foamable resinadhesive:

    ______________________________________    Constituent   Weight Percent    ______________________________________    PG 76-120     73-76%    R 420         20-22%    L 5420        1.5%    33 LV         0.6%    H.sub.2 O     2.2%    ______________________________________

33 LV is an amine catalyst available from Union Carbide Chemical &Plastics Co. As will be understood by those skilled in the art,adjusting the polyether polyol ratio and adding an amine catalyst makesthe foam formulation "hotter", providing a good foam bead at colderambient temperatures. The A iso side of the formulation may be the sameas the formulation described above.

The green sheer strength of the described foam resin adhesive utilizedin the method of this invention is as follows:

    ______________________________________           Time  Sheer Strength    ______________________________________           10 min.                 117.00 psi           11 min.                 121.30 psi           13 min.                 136.80 psi           17 min.                 199.00 psi           20 min.                 254.80 psi           24 hrs.                 604.30 psi    ______________________________________

Thus, the reinforced panel assembly formed- by the method of thisinvention can be picked up and handled by conventional material handlingtechniques within a few minutes after bonding.

After the foam bead 28 is applied, as shown in FIG. 1 at 28a, the beadis allowed to substantially fully cream and rise, forming an enlargedfoam bead on the surface 29 of the structural support members which areto be bonded to the finish panel 50. As shown in FIG. 4, the finishpanel 50 may be applied on top of the bead and pressed. More preferably,the first panel assembly 20 may be turned as shown in FIG. 5 and thesupport members applied to the finish panel supported on a flat surface,such as a vacuum table 52. In either method, the volume of the bead 28bshould be sufficient to completely bridge the mating surfaces of thefinish panel 50 and the structural support members 22 as shown in FIG.4. Where a flat finish panel is desired, the panel is first laid on aflat support surface, such as the vacuum table 52 shown in FIG. 5. Avacuum table having a plurality of holes 54 may be desired where thepanel is relatively flexible, but is warped or includes "wows". Vacuumtables are commonly used to maintain a flexible sheet, board or panelflat while it is being worked upon.

As stated above, FIG. 5 illustrates a preferred embodiment of the methodof this invention. As shown, the first panel assembly 20 is turned orrotated, such that the beads 28 overlie the finish panel 50, which issupported on the vacuum table 52, as described above. The first panelassembly 20 is then pressed against the finish panel, compressing thebeads 28 against the finish panel. The polyurethane foam then wets thefinish panel, forming a bridge between the finish panel 50 and thestructural support members 22, as shown in FIG. 4. Thus, it is necessaryto complete this step before the polyurethane foam beads fully cure tackfree. Further, the polyurethane foam beads must be sufficiently flexibleto bridge the interface between the structural members and the finishpanel. The completed structural panel assembly may be lifted and handledalmost immediately upon pressing of the structural members 22 againstthe finish panel. That is, the bonding is almost instantaneous, which isan important advantage of the method of this invention.

FIGS. 6 and 7 illustrate structural panel assemblies formed by themethod of this invention. As described above, the finish panel 50 ispreferably first laid upon a flat surface 51. In the disclosedembodiment, the flat surface is provided by a vacuum table 52 having aplurality of spaced holes 54. A vacuum is drawn on the underside of thetable 52 which draws the panel 50 against the flat surface 51, ironingout any warpage or "wows" in the flexible panel 50. FIG. 6 illustrates acommon situation where the structural support members 22 are ofdifferent widths. As stated above, the structural support members 22 arecommonly 2×4's or 4×6's as used for studs in wall panel assemblies,joists in flooring assemblies and trusses in ceiling assemblies. Thedimensions of such lumber, however, vary significantly. The long sidemay vary as much as 1/2 inch. As shown, however, the foam bead 28 fillsin the additional space required by the thinner structural members, suchthat the finish panel 50 remains completely flat. FIG. 7 illustrates thesituation where the structural member 22 is warped or bowed. As shown,the foam bead 28 will similarly fill the concave areas, such that thefinish panel 50 remains flat. As described, the finish panel is retainedflat on the vacuum table 52 when the first panel assembly is turned andapplied to the finish panel, as shown in FIG. 5.

FIGS. 8 and 9 illustrate a mixing chamber 60 of the foam application gun30 of FIG. 1. The mixing chamber 60 includes a cylindrical body 62having an axially bore 64 which defines the mixing chamber. The end 66is externally threaded to receive a nozzle (not shown) and the oppositeend is counterbored at 68 to receive a ferrule 72 and internallythreaded to receive a packing or lock nut 70. A valve rod 76 isreciprocated in the axial bore 64 by the pneumatic cylinder assembly 38of FIG. 1 as described below.

When the value rod is retracted, the A and B components of the foamresin adhesive enter the mixing chamber 64 separately through very smallslots 82 on opposite sides of the valve body 62. Hardened inserts 80 maybe provided to reduce wear. The slots have a width of about 1/2 thediameter of the bore mix chamber 64, such that the high impingementforce of the foamable resin components entering the chamber isdissipated sufficiently to generate a low velocity bead, as describedabove. In an actual embodiment, the width of the slot 82 was 0.046inches and the diameter of the bore mixing chamber 64 was 0.078 inches.The viscosity of the A iso side was 250 cps and the B polyol side was560 cps. The inlet pressure was 400 psi. The A and B components werethoroughly mixed in the high impingement mixing chamber and exited thebore at about 3 feet per second, forming a relatively thin bead offoamed resin adhesive without splatter, as described above.

The foam application gun 30 shown in FIG. 1 is operated by actuating thetrigger mechanism 36, which operates the pneumatic cylinder to retrackthe valve rod 76 beyond the slot 82, permitting the A iso and B polyolcomponents of the foamable resin to enter the mixing chamber 64 underhigh impingement pressure, where the components are thoroughly mixed.The foamable resin adhesive then exits the outlet 86 of the mixingchamber, where it is applied in the form of a thin liquid bead 28a asshown in FIGS. 1 and 2. Almost immediately, the liquid bead creams andrises, forming the foam beads 28b and 28c as shown in FIGS. 1 and 3. Theapplication gun 30 may be hand-held or the gun may be supported on amovable fixture and computer-controlled, for example. Where the gun iscomputer-controlled, it may be preferred to apply the foam beads firstto the finish panel 50. The structural support members may be secured toa first panel 24 as shown in FIG. 1, or the structural support members22 may be oriented and supported in a jig or fixture, eliminating therequirement for a first panel in a floor assembly, for example.

The foam 28 preferably substantially fully bridges the interface betweenthe structural support members 22 and the finish panel 50 ae shown inFIG. 4, such that the finish panel 50 does not contact the structuralsupport members 22. The cellular foam adhesive provides a resilientjoint between the structural support members and the finish panel and athermal break. These advantages are provided even where the foam bead isinterrupted at predetermined locations to reduce cost.

As will be understood by those skilled in the art, various modificationsmay be made to the method of forming structural panel assemblies of thisinvention and the resultant improved rigid structural panel assemblywithin the purview of the appended claims. For example, the structuralsupport members 22 may be attached to the first panel 24 by any suitablemeans, including mechanical fasteners, although the use of foamadhesives had several advantages over the prior art, as described above.Further, although an important advantage of the method of this inventionis the elimination of mechanical fasteners, mechanical fasteners mayalso be used between the finish panel and the structural supportmembers. Finally, although the foam resin bead is preferably applied tothe structural members, as described above, the bead may alternativelybe applied first to the finish panel.

I claim:
 1. A method of forming a self-supporting structural panelassembly comprising a plurality of support members permanently bonded toa generally flexible fibrous panel, said support members being generallyrectangular in cross-section each having a pair of opposed generallyparallel side surfaces and a pair of opposed generally parallel edgesurfaces, with said edge surfaces being narrower in width than said sidesurfaces, said method comprising:arranging a plurality of said supportmembers in generally parallel relation to each other such that one ofsaid edge surfaces of each of said plurality of support members isoriented upwardly to form a top surface of each of said support memberswith said top surfaces of said support members being generallyco-planar; applying a bead of a liquid foamable polyurethane resinadhesive along the length of each of said top surfaces of each of saidsupport members with said bead having a width substantially less thanthe width of each of said top surfaces of each of said support members;applying said flexible fibrous panels to said top surfaces of saidsupport members under pressure thereby compressing said beads of saidliquid foamable polyurethane resin adhesive and wetting the opposedsurfaces of each of said top surfaces of said support members and theopposed surfaces of said flexible fibrous panels and said liquidfoamable polyurethane resin adhesive foaming and rising and fillingvoids between said flexible fibrous panels and said top surfaces of saidsupport members; and allowing said liquid foamable polyurethane resinadhesive to cure thereby permanently bonding substantially the entiresaid top surface of each of said support members to the opposed surfacesof said flexible fibrous panels and forming a self-supporting structuralpanel assembly.
 2. The method of forming a self-supporting structuralpanel assembly as defined in claim 1, wherein said method includesthoroughly mixing said liquid foamable polyurethane resin adhesiveimmediately prior to applying said bead of said liquid foamablepolyurethane resin adhesive along the length of each of said topsurfaces of each of said support members.
 3. The method of forming aself-supporting structural panel assembly as defined in claim 1, whereinsaid method includes compressing said beads of said liquid foamablepolyurethane resin adhesive wetting substantially the entire width ofeach of said top surfaces of each of said support members and theopposed surfaces of said flexible fibrous panel.
 4. The method offorming a self-supporting structural panel assembly as defined in claim1, wherein said liquid foamable polyurethane resin adhesive comprises athixotropic liquid foamable polyurethane resin adhesive; wherein saidmethod includes applying a bead of said thixotropic liquid foamablepolyurethane resin adhesive along the length of each of said topsurfaces of each of said support members with said bead having a widthsubstantially less than the width of each of said top surfaces of eachof said support members.
 5. The method of forming a self-supportingstructural panel assembly as defined in claim 1, wherein said liquidfoamable polyurethane resin adhesive comprises a plural component liquidfoamable polyurethane resin adhesive; wherein said method furthercomprises thoroughly mixing the components of said plural componentliquid foamable polyurethane resin adhesive immediately prior toapplying said bead of said plural component liquid foamable polyurethaneresin adhesive along the length of each of said top surfaces of each ofsaid support members with said bead having a width substantially lessthan the width of each of said top surfaces of each of said supportmembers.
 6. A method of permanently bonding a plurality of flexiblefibrous wall panels to a plurality of studs to form a rigid enclosedstructural wall panel assembly, said method comprising the followingsteps:making a first wall panel assembly comprising a first wall paneland said plurality of studs, said studs being aligned generally parallelto each other and connected to said first wall panel and extending froma surface of said first wall panel, and orienting and supporting saidfirst wall panel assembly in an orientation to be bonded to a secondwall panel, each of said plurality of studs having a generally flat edgesurface, which is to be bonded to said second wall panel; applying abead of a liquid foamable polyurethane resin adhesive along the lengthof each of said edge surfaces of each of said studs with said beadhaving a width substantially less than the width of each of said edgesurfaces of each of said studs; applying under pressure said second wallpanel to said edge surfaces of said studs with said beads of said liquidfoamable polyurethane resin adhesive, thereby compressing said beads ofsaid liquid foamable polyurethane resin adhesive and wettingsubstantially the entire width of said edge surfaces of said studs andthe opposed surfaces of said second wall panel and said liquid foamablepolyurethane resin adhesive foaming and rising and filling voids betweensaid second wall panel and said edge surfaces of said studs; andallowing said liquid foamable polyurethane resin adhesive to curethereby permanently bonding substantially the entire width of said edgesurface of each of said studs to the opposed surfaces of said secondwall panel and forming a rigid enclosed structural wall panel assembly.7. The method of forming a rigid enclosed structural wall panel assemblyas defined in claim 6, wherein said method includes thoroughly mixingsaid liquid foamable polyurethane resin adhesive immediately prior toapplying said beads of said liquid foamable polyurethane resin adhesivealong the length of each of said edge surfaces of said studs.
 8. Themethod of forming a rigid enclosed structural wall panel assembly asdefined in claim 6, wherein said liquid foamable polyurethane resinadhesive comprises a thixotropic liquid foamable polyurethane resinadhesive; wherein said method further comprises applying a bead of saidthixotropic liquid foamable polyurethane resin adhesive along the lengthof each of said edge surfaces of each of said studs with said beadhaving a width substantially less than the width of each of said edgesurfaces, then applying under pressure said second wall panel asdefined.
 9. The method of forming a rigid enclosed structural wall panelassembly as defined in claim 6, wherein said liquid foamablepolyurethane resin adhesive comprises a plural component liquid foamablepolyurethane resin adhesive; wherein said method further comprisesthoroughly mixing the components of said plural component liquidfoamable polyurethane resin adhesive immediately prior to applying saidbeads of said plural component liquid foamable polyurethane resinadhesive along the length of each of said edge surfaces of said studswith said beads each having a width substantially less than the width ofeach of said edge surfaces.
 10. A method of forming a self-supportingwall panel assembly comprising a plurality of support memberspermanently bonded to a generally flexible fibrous wall panel, saidsupport members each being generally rectangular in cross-section eachhaving a pair of opposed generally parallel side surfaces and a pair ofopposed generally parallel edge surfaces, with said edge surfaces beingnarrower in width than said side surfaces, said methodcomprising:arranging a plurality of said support members in generallyparallel relation to each other such that one of said edge surfaces ofeach of said plurality of said support members is oriented in generallyco-planar relation; applying a bead of a liquid foamable polyurethaneresin adhesive generally along the length of said co-planar edgesurfaces of said plurality of support members with said bead having awidth substantially less than the width of said co-planar edge surfacesof each of said support members; applying said flexible fibrous wallpanel to said co-planar edge surfaces of said support members underpressure thereby compressing said beads of liquid foamable polyurethaneresin adhesive and thereby wetting and substantially bridging saidco-planar edge surfaces of said support members with liquid foamablepolyurethane resin adhesive and wetting the opposed surfaces of saidflexible fibrous wall panel and said liquid foamable polyurethaneadhesive foaming and rising and filling voids between said flexiblefibrous wall panel and said co-planar edge surfaces of said supportmembers; and allowing said liquid foamable polyurethane resin adhesiveto cure thereby permanently bonding said co-planar edge surfaces of saidsupport members to the opposed surfaces of said flexible fibrous wallpanel and forming a self-supporting structural wall panel assembly. 11.The method of forming a self-supporting panel assembly as defined inclaim 10, wherein said method includes thoroughly mixing said liquidfoamable polyurethane resin adhesive immediately prior to applying saidbead of said liquid foamable polyurethane resin adhesive along thelength of each of said top surfaces of said plurality of supportmembers.
 12. The method of forming a self-supporting panel assembly asdefined in claim 10, wherein said liquid foamable polyurethane resinadhesive comprises a thixotropic liquid foamable polyurethane resinadhesive; and wherein said method further comprises applying a bead ofsaid thixotropic liquid foamable polyurethane resin adhesive along thelength of each of said top surfaces of each of said plurality of supportmembers with said bead having a width substantially less than the widthof each of said top surfaces.
 13. The method of forming aself-supporting panel assembly as defined in claim 10, wherein saidliquid foamable polyurethane adhesive comprises a plural componentliquid foamable polyurethane resin adhesive; wherein said method furthercomprises thoroughly mixing said plural component liquid foamablepolyurethane resin adhesive immediately prior to applying said beads ofsaid plural component liquid foamable polyurethane resin adhesive alongthe length of each of said top surfaces of each of said plurality ofsupport members with said beads each having a width substantially lessthan the width of each of said top surfaces of each of said supportmembers.